1. Field of the Invention
This invention is directed to enhancements to traditional Ethernet functionality and in particular to a high speed (HS) Ethernet based on SONET technology:
2. Background Art
For the last decades, the industry has evolved from voice circuit switching to data message switching, then to data oriented packet switching. In the past years, other technologies have been introduced into the marketplace to enhance or supplant these older technologies, such as frame relay, fast Ethernet, switched Ethernet, and ATM. Yet even some of these technologies do not solve the current problems; frame relay is fundamentally for wide area network (WAN) technology and fast Ethernet and switched Ethernet are for local area network (LAN) technologies.
In 1984 CCITT adopted the first I-series Recommendations which was a milestone in the development of integrated services digital networks. These Recommendations are concerned with services, network-network interfaces (NNI), user-network interfaces (UNI) and overall network aspects.
OSI (open system interconnection) is a reference model defining a seven-layer framework of protocols for data communications, designed with the purpose to allow any computer anywhere in the world to communicate with any other, as long as they obey the OSI standards. Layering divides the total communications problem into smaller functions, while ensuring independence of each layer from the next layer, by defining services provided by a layer to the next layer, independent of how these services are performed.
The lowest layer is the physical layer (PHY), covering the physical interfaces between the devices, and is concerned with transmitting raw bits over communication channels, and informing layer two (Data Link) of loss of connectivity. Physical layer functions are for example add, drop and multiplexing of traffic. The add/drop multiplexer (ADM) can multiplex/demultiplex any of its various tributary inputs into/from a line signal and it can be used as a hub, an ADM, or a terminal. When used as an ADM, it only accesses signals that need to be dropped or added at that site, the rest of the traffic passes straight through.
An important task of the data link layer (second layer) is to break data into frames, to then transmit these frames sequentially and, in some cases, to process acknowledgement frames sent back by the receiver. The network layer (the third layer) provides the functional and procedural means to set-up and terminate a call, to route data and to control the data flow across the network. The remaining layers are application oriented, being concerned with providing various service functions to the users, such as session control, network management, and other services.
Some technologies are more appropriately applied at certain layers. For example, SONET is a physical layer technology and is used as a transport service for ATM, SMDS, frame relay, T1, E1, etc, while ATM operates on SONET, copper, twisted pairs, FDDI as physical layer, the data layer being subdivided into an ATM layer and an ATM adaptation layer.
Local area networks (LANs) connect personal computers to one another and to shared machines. Both general purpose computers called hosts or clients, and special purpose computers called servers, provide communal files, e-mail, etc.
The oldest and best known LAN is the Ethernet, which in many cases operates on FDDI (fiber distributed data interface) physical layer, and a media access control (MAC) layer, placed on top of FDDI, comprises the data layer.
The IEEE became involved in setting standards for LANs under 802 committee, and assumed a role in leading LAN standards bodies. Ethernet was published as IEEE 802.3 designed for data applications is based on a shared bus in which all stations on the network share the media.
A wide area network (WAN) is a packet switched public data network that connects various packet switching nodes and transmission facilities to customer premises equipment (computer stations). A WAN differs from the LAN in geographic coverage and data rates, and also in technology.
The metropolitan area network (MAN) technology differs from the LAN and WAN in geographic coverage and data rates. A MAN could be owned by an organization, or could be public, and enables users to share efficiently widely distributed resources. A MAN could also serve as a backbone of a network that interconnects distributed LANs. Currently, the MAN evolves towards WAN technologies in the backbone, due to the increased demand in data communication.
It has become evident that LAN shared bus architecture is insufficient to meet the demands of applications that require more bandwidth, and that LANs are beginning to become a bottleneck in computing environments. For this reason, the separation of data into cells is deferred until within the network, but the higher level information is carried to the end station.
Switched Ethernet technology, developed to provide more capacity to an end-user, does not rely on shared medium, it rather provides point-to-point bandwidth between the user station and the switch, so that instead of sharing a 10 Mbit/s medium, the user gets a dedicated 10 Mbits/s medium. A switched Ethernet network is more flexible, in that it may include stations that are using a port at a given full rate, stations that share a port, or stations that have access to more than one port.
However, switched Ethernet provides only limited bandwidth and supports data traffic only. As Ethernet hubs and switches are growing in use, they become an inexpensive means to provide more bandwidth to workstations. A more efficient solution for bursty traffic is needed. There is also a need to simplify and standardize the access link while also providing protection of the access traffic.
Nonetheless, of great concern for network providers in the era of the data transmission is the LAN performance at higher speeds. 10 Gb/s market is emerging fast in campus backbone networks.
In addition, several existing problems cannot be solved by the current solutions. For example, the LAN bandwidth is currently provisioned in a rigid manner, while many users need scaleable bandwidth for different applications.
It would be highly beneficial to have a uniform architecture for LANs, MANs and WANs, by seamlessly bridging the LAN technology onto MAN and WAN through the same frame protocol and transmission technology.
The dominant signal format in the fiber optic networks follows the synchronous standard SONET in North America and SDH elsewhere. In this specification, SONET is defined to include SDH. SONET enables the multiplexing, adding and dropping and general transportation of signals through these networks.
For a service, being able to be easily transported by a SONET network is a valuable attribute, in that the network provider can make use of the large base of installed SONET-compatible equipment. As well, SONET provides the ability to combine and consolidate traffic from different locations through one facility (grooming), and reduces the amount of back-to-back multiplexing. More importantly, network providers can reduce the operation cost of their transmission network by using the operation, administration, maintenance and provisioning (OAM&P) features of SONET.
Mapping of one rate or format into another is well known. Bellcore GR-232 describes in detail the standard mappings of the common asynchronous transmission formats (DS0, DS1, DS2, DS3, etc) into SONET. Similar mappings are defined for the ETSI hierarchy mapping into SDH. Optical transmission equipment designed for mapping one proprietary format into another is also available on the market, e.g. Nortel's FD-565 could carry the FD-135 proprietary format as well as the DS3 standard format.
As a physical carrier technology and also due to the advantages listed above, SONET looks as a candidate of choice for carrying Ethernet. No attempts are known to the applicants that efficiently map Ethernet into a SONET container to take advantage of the SONET features and of the installed base of SONET equipment. There is a need for an efficient method to map Ethernet signals into SONET such that the signals can be recovered with low timing jitter and inexpensive hardware.